How to prevent unnecessary Windows 10 Update re-installation?

Sometimes, even after Windows ISO was properly updated and fully rebased with W10UI (4.5) to have the latest SS, Flash, NetFX (4.7.1), and CU, Windows Update still re-downloads and re-applies the latest CU. Why does it do that and how do I prevent that? For an average user who doesn't know anything about OS imaging, is there any point to have an ISO with the latest updates integrated, assuming that Windows Update will re-download and re-apply the latest CU anyway?

I know it's normal for Windows Update to do that if NetFX 3.5 is installed after CU was applied to the image, but that was not the case. NetFX 3.5 was not used/installed/touched in any way before or after the latest CU was applied on neither offline or online/live installation...

Zero butchering on that one, no NTLite, no MSMG Toolkit, no NetFX 3.5, just W10UI + SS, CU, Flash, NetFX 4.7.1 and NetFX 4.7.1 Update... Sometimes it downloads just a bit of the latest CU, but other times the whole damn thing...